The long answer: They're "obsequious and needy" "middlemen" who find people looking to invest money.

Levine said that I-bankers are "selling money to companies" by encouraging those companies to issue stocks and bonds for investors to buy. While sales and traders actually sell the securities to investors, I-bankers arrange for them to be sold.

When those securities are purchased, the company can then use investor money to expand by hiring new workers or building new factories for instance.

Levine writes:

"When a company decides to issue stock or bonds, investment bankers perform 'due diligence' to make sure the company's accountants will say that the company's financial statements say what they say they say."